Planetary screw drives (PSDs) (also referred to as planetary roller screw drives) have been the state of the art for many years, and are described, for example, in DD 0277308 A5. A planetary screw drive is known, for example, from published patent DE 10 2010 047 800 A1, which is contained in a hydrostatic actuator in the form of a hydrostatic clutch actuator in order to convert a rotary motion produced by means of an electric motor to an axial motion. A planetary screw drive having a screw spindle and having a nut situated on the screw spindle and having a plurality of planet gears distributed around the circumference, positioned between the screw spindle and the nut, which are arranged so that they can roll on the inside circumference of the nut as well as on the outside circumference of the screw spindle, is known from published patent DE 10 2010 011 820 A1. In this solution, a pre-stressing device is provided for the planet gears, wherein the nut has two parts that are movable axially relative to each other, and wherein the pre-stressing device has a spring element that is spring loaded against the one nut part. The nut assumes two functions: on the one hand it is part of the transmission and on the other hand it is part of the pre-stressing device.
It is also known (see DE 10 2011 088 995 A1) to perform an absolute measurement to register the slip of a PSD having a screw spindle and having a spindle nut situated on the screw spindle and having a plurality of planet gears distributed around the circumference, where a sensor element that is positioned axially immovably relative to the spindle nut registers an axial displacement of the screw spindle and the spindle nut relative to each other, the spindle nut being supported on a housing that has the sensor element so that it can rotate around the spindle axis.
A yet unpublished application describes a disengaging system for a clutch of a motor vehicle, wherein while using a drive a supported piston is actuated so that it is movable axially in a housing by means of a PSD.
The known systems require a large axial construction space, and turn out to be relatively expensive.
Known central clutch releases used in disengaging systems, such as electric clutch releases for example, are built relatively compactly, but are not closed axially and have an essentially ring-shaped structure.